1. Field of the Invention
The present invention relates to antenna arrangements for suppressing selected sidelobes and, more particularly, to antenna arrangements comprising a focusing reflector, a main feed arrangement and at least two auxiliary feed arrangements disposed on opposite sides of, and a predetermined equal distance from, the main feed arrangement in the plane of the selected sidelobes to be primarily suppressed. By proper adjustment of the phase, amplitude, direction and transverse off-axis distance of the auxiliary feed arrangement with respect to the main feed arrangement, the selected sidelobes will be suppressed.
2. Description of the Prior Art
In radar systems and in terrestrial and satellite communication systems, various techniques have been used to reduce certain sidelobes and in turn the interference therefrom in adjacent links. In receiving systems, undesired sidelobe signals are generally suppressed by receiving the desired signal at a directional antenna and possible interfering signals at a separate omnidirectional antenna. The derived interfering signals are then used to cancel interference in the desired signal using various circuitry configurations. In this regard see, for example, U.S. Pat Nos. 3,094,695 issued to D. M. Jahn on June 18, 1963 and 3,202,990 issued to P. W. Howells on Aug. 24, 1965.
Alternatively, for transmission purposes U.S. Pat. No. 3,704,464 issued to C. J. Drane, Jr. et al on Nov. 28, 1972 discloses a method for maximizing aerial directive gain while simultaneously placing nulls in the far-field radiation pattern of an array of N elements which are arbitrarily positioned. The patented method permits specification of directions of up to N-1 independent pattern nulls and/or sidelobes while assertedly providing maximum gain in some prescribed direction. This control is apparently achieved by varying only the amplitude and phase of the element currents in association with a standard gain formula.
U.S. Pat. No. 3,815,140 issued to W. E. Buehler et al on June 4, 1974 relates to a multiple feed arrangement for microwave parabolic antennas which include a parabolic reflector, and a plurality of individually fed illuminators. Each illuminator alone produces a beam of certain dimensions, and by combining the beams through the use of a predetermined configuration of illuminators, including their number and spacing, the physical configuration of the beam, including sidelobes, may be accurately controlled. Furthermore, certain illuminators may be fed by different information sources, thus resulting in a multiple information beam pattern.
The problem remaining in the prior art is to be able to provide antenna arrangements which produce low sidelobes in selected directions to provide minimal interference in certain links using simple techniques.